The Chicago Democrat is one of several state lawmakers confronting stiff challenges in the March 18 primary election because of risky, high-profile votes for cutting state worker retirement benefits or legalizing gay marriage. The votes triggered unions or other interest groups to actively work against their re-election bids.

Fearful that lawmakers will next turn to cutting municipal employee pensions, state employee unions and the Chicago Teachers Union have poured hundreds of thousands of dollars into the campaign of Mitchell's challenger, Jhatayn "Jay" Travis.

In turn, Mitchell has been backed by donations from the House Democratic leadership and an education reform group, which have helped paid for TV commercials and mailing pamphlets to voters.

"I couldn't keep up otherwise," Mitchell said.

The targeted challenges are among the toughest primary races in a year in which all 118 House seats and a third of 59 Senate seats are up. Overall, there are 27 primary contests for House seats this month, but just two in the Senate.

While Democrats stand a good chance of holding onto their veto-proof supermajorities in both legislative chambers this year, the intra-party challenges and interest group influence could alter the makeup of each caucus, experts say, with potentially fewer moderates on the ballot come November. The Democrats have 71 seats to Republicans' 47 in the House, and a 40-19 margin in the Senate.

"It wouldn't surprise me for the Democrats to lose a few seats in the House, but it's likely to be because of multiple factors," University of Illinois Springfield Professor Emeritus Kent Redfield said. "The pension thing does not help."

Redfield said the tighter races may hinge on which candidates have the most mobilized supporters, meaning more advantage for the unions, which are "very good at the get-out-the-vote, ground-game kind of stuff."

The state's largest public employees union, AFSCME, is teaming with other unions to target at least three Democratic incumbent House members from Chicago — Mitchell, Toni Berrios and Jaime Andrade, Jr. All voted for the pension legislation and are viewed as vulnerable.

They've been targeted through campaign donations to their rivals, door-to-door canvassing and direct mail to voters.

"We think there is a real chance to elect challengers who are independent of the political machine and who can defeat incumbents who were wrong on retirement security and have voted for pension cuts," AFSCME spokesman Anders Lindall said.

In Mitchell's 26th District, which stretches from the downtown Streeterville neighborhood to the city's less affluent South Side, the Chicago Teachers Union, the American Federation of Teachers, AFSCME and others have spent more than $300,000 helping Travis, a community organizer. She argues that Mitchell's pension vote did not reflect the wishes of his district.

"I don't know that it's as much retaliation as people wanting to make sure their elected representation represents their interest," Travis said.

But Mitchell has received more help as the battle intensifies. The Democratic Majority fund — one of the main funds for House Democrats, controlled by House Speaker Michael Madigan— added $30,000 to Mitchell's campaign coffers in the past three weeks to help with pamphlet mailings, and fellow Democratic lawmakers have collectively thrown $20,000 into Mitchell's war chest over the last month.

He also has received $45,000 from the education reform group Stand for Children, the largest check the organization has written to any legislative candidate during the primary campaign, and he has collected money from a number of wealthy Chicago businessmen.

On the gay marriage issue, a threatened campaign by ministers against Democrats did not materialize after the November vote to make Illinois the 16th state to allow it.

But on the GOP side, two of the toughest primary challenges involve state Reps. Ron Sandack of Downers Grove and Ed Sullivan of Mundelein, two of three House Republicans who broke ranks to vote in favor. The third, former House Republican leader Tom Cross, gave up his seat to run for treasurer.

Sandack is being challenged by Downers Grove High School teacher Keith Mathune and Sullivan by Mundelein bus driver Bob Bednar. Both are being helped by conservative family groups hoping the four-way GOP governor primary lures social conservatives to the polls.

Illinois Families First, a political action committee started by conservative activist Paul Caprio, is working with local religious groups to campaign against Sandack and Sullivan — including raising money and organizing robo-calls.